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If a player makes an active Perception check and the result is lower than their passive Perception score, should we use the passive Perception score instead?
Background:
During our weekly game yesterday the party scout was actively searching for hidden monsters. He rolled poorly and ended up with a 7 on his Perception check, seeing nothing. The claim was then made that since his passive Perception score was 15, he would intuitively notice anything that he didn't actively spot.
The party scout was correct. Passive perception does not "turn off" when you are actively searching. It only stops if you are unconscious. You always notice anything that hasn't beat your passive perception score — even if you aren't actively searching.
You can also take actions to actively search, giving you an opportunity to sense things you haven't already noticed.
For example, if your passive Wisdom (Perception) score is 15, and a monster is lurking with a Dexterity (Stealth) roll of 14, you notice them without rolling. If the monster got a 15 or higher, though, they've beaten your passive senses. Let's say that the monster has a modifier of +3 and rolled 16 on the die, for a result of 19. In this case, on your turn, you can take actions to actively search, for which the DM can call for Wisdom (Perception) rolls. If you exceed the monster's total, you've noticed it. If you get the same total or less (19, here) the situation remains the same and the monster is undetected. For that first monster — the one with a 14 total Dexterity (Stealth) check — the situation also remains the same, which is that you've already noticed them. They aren't somehow "de-noticed".
Jeremy Crawford explains in the Sage Advice section of this podcast, starting at about 15:09.
JC (at 22:16): Now, going back to passive perception... this is, as its name implies, passive. And, it's considered to be "always on", unless you're under the effect of a condition, like the unconcious condition that says you're not aware of your surroundings. That really... the practical effect of that is that basically your passive perception is shut off. Passive perception is on basically whenever you are conscious and aware. [...]
JC (at 23:09): Because it's passive, the player does not get to say they use it. This is a... this is something that people...
Interviewer: (Laughs) I'm using my passive perception right now!
JC: Yeah, no. It's always on. That's the baseline. Now, this brings up questions, because then people are saying that, well, how is it that when I make an active perception check, I might get a roll that's lower? Well, you aren't... yes, that roll is lower, but remember your passive perception is aways on. So it really represents the floor of your perception.
Interviewer: Right. That's an important distinction, though.
JC: Yes. So if you make an active perception check and you get a number that's lower than your passive perception, all that means is that you did a lousy job of this particular active search, but your passive perception is still active. You're still going to notice something that "blips" onto your passive perception radar. Really, when you make that roll, you're really rolling to see "can I get a higher number?" If you fail to, well, again, your passive perception score is still active. It is effectively creating that minimum.
Interviewer: The minimum. Yeah, I don't know if that's necessarily clear to a lot of dungeon masters out there, because they will be like, well, the opposed nature of this roll means that you were just really bad at looking, and even though the person who is sneaking up on you only got like a five, they're able to do so.
JC: Now, many of these sorts of situations would be erased if DMs just simply remembered to use the passive perception in the first place. Because honestly, if something's noticable by a person's passive perception score, they should already have noticed it. So really, the active search is trying to find something that you haven't already noticed, and your passive perception score represents what you have already noticed.
(Bold added to highlight the key points; italics intended to represent emphasis in the speech.)
Yes, but in reverse. You should check passive perception first and note that the DCs for passive and active perception may be different.
Passive Perception often sets the floor. Basically, a lot of the time you're rolling (i.e., active perception) to see if you can roll higher than a 10 and do better than with your passive perception.
Clarification: If your passive perception meets the DC, you shouldn't be rolling. When you roll for active perception, you do so because you didn't already passively perceive something. Thus, only roll for active perception if you need to roll a 10 or better.
However, there is at least one officially-released adventure that suggests that actively looking is sometimes easier than passive perception. In the Lost Mine of Phandelver, the passive perception DC is 15 but drops to 10 for active perception (i.e., PCs start actively looking for something rather than relying on their passive skills):
Secret doors are made of stone and blend in with the surrounding walls. Spotting a secret door from a distance of no more than 10 feet without actively searching for it requires a passive Wisdom (Perception) score of 15 or higher, whereas a character who takes the time to search the wall can find the secret door with a successful DC 10 Wisdom (Perception) check. Secret doors swing open on hidden iron hinges and are not locked.
Part 2. Phandalin, pg. 20 of Lost Mine of Phandelver
Hopefully, the DMG will elaborate on this mechanic. A quick thumb-through the HOTDQ and the rest of the starter adventure don't reveal any other instances of this (there's only one secret door in HOTDQ and no more in the starter set).
First off, there is no rule in the game that states passive checks set a floor to active checks. Passive Checks are defined on p. 175, PHB:
A passive check is a special kind of ability check that doesn’t involve any die rolls. Such a check can represent the average result for a task done repeatedly, such as searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster.
A single active check is not something done repeatedly, and obviously is not something the DM is trying secretly -- the player is actively taking a check, they are fully aware of it. The rule for passive checks simply does not apply to a situation where you are making an active check.
So, the only rationale for allowing the passive check to set a floor to perception is not rules-as-written based. It is based on a common sense argument: the player's character would notice something without even trying. Ergo for a given difficulty, they should not fail on it if they are actively trying, because they should be able to do it better if they put effort to it.
However, there are several counterpoints to that view:
From a real world psychological point of view, focusing your attention on something may make you blind to other things that you might otherwise notice -- the best-known example is the famous Selective Attention Test. If you do not know it, go ahead and try it, its fun. So, if a character is for example actively looking for cracks that might indicate a secret door, they may miss some other telltale sign they might have caught if they were not even looking.
Secondly, there are features like the Rogue's Reliable Talent that effectively set a floor to a skill in the same way allowing a passive check to do so would, and also for skills that could be done passively. For example, the Inquisitive Rogue has a feature called Ear for Deceit that states:
Whenever you make a Wisdom (Insight) check to determine whether a creature is lying, treat a roll of 7 or lower on the d20 as an 8.
This feature would be entirely worthless if passive checks could set a floor in general -- the passive check would set a floor of 10, not 8, so would be better. The existence of this feature is a good indicator that passive checks are not necessarily meant to set a floor.
So, while you can make a common sense argument to allow this as a DM, there is no direct rules support for it, there are conflicts with other rules, and it can have undesirable side effects.
Does passive perception supersede active perception?
It can look like it does because of how some cases work out, but as a rule, no, it doesn't.
Passive perception covers two different things:
PHB p.175:
A passive check is a special kind of ability check that doesn’t involve any die rolls. Such a check can represent the average result for a task done repeatedly, such as searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster.
Perception checks, i.e. actively looking (I ma not going to use the term active perception checks as they are just normal perception checks), cover the case where a creature is actively and discretely (i.e. not over a large number of rolls) looking for something. It differs from the passive perception case in that the creature has been given reason to search for something hidden right here, right now, even though it has not seen it yet just by being in the scene, i.e. with its passive perception.
This reason for actively looking may be that they "just have a feeling", it might be that it looks like a good spot for an ambush/trap etc. or it may be that they somehow know the thing they are looking for is here but they haven't noticed it yet. It can be anything, but there has to be a reason they think actively searching its required to make a perception roll. Effectively the player must ask the DM for a perception roll, even if it is done indirectly through a player describing the actions of a character and the DM deciding that requires it.
Passive perception is therefore not simply the minimum value a creature can "roll", due to the fact that there is no reason that the hidden thing has the same DC for passive and active perception checks, or that it is available for passive perception checks at all,. In addition a creature actively looking gives up a measure of their general awareness by focusing on the search and thus their passive perception is replaced by the results of the roll, at least for the thing being looked for. A bad roll represents looking in the "wrong" place or similar.
Examples:
Why would case 4 ever happen? It represents a trade off made by the rogue's player, balancing the chance to notice traps too well hidden for their passive perception (cases 1 and 2) against the chance to miss traps they would have noticed just by standing at the doorway, i.e. its a bet by the player that they will roll well enough to see something hidden that the character can't see with their passive perception.
As a last note, without wanting to go into the differences between investigation and perception, passive investigation vs active investigation would follow the same general principles.
If your passive Wisdom (Perception) check was high enough to detect a hidden secret, trap or enemy, the DM should have already delivered that information, so a roll from an active check less than or equal to your passive check simply doesn't provide any more information.
In the absence of any discussion or ruling in the DMG for 5E, it's going to be a judgement call on the part of the DM.
However there's no point in rolling if you have no chance of failure, so I'd argue that an active roll always supersedes a passive check.
That said, there are a number of ways to explain away a poor result.
One is that the signs were noticed, but dismissed as something else (the old "oh, it's just a cat" trick).
Another is to have an active deception divert attention (the old "throw a rock into the bushes over there to distract the guard" trick).
You can even have them succeed, but just a moment too late to warn everyone (the old "quiet, I heard something over - ARGH!" trick).
Really the important thing is to couch a failure in terms of 'success at the wrong thing' or 'something interferes' rather than 'you see nothing'.
In the example, the scout should have seen a potential ambush, with no need to roll, if his passive score was sufficient. The fact that he asked to make an active roll doesn't change that. He certainly shouldn't be punished for taking extra care.
Barring exceptional circumstances (the PC is blindfolded, or the PC is hugely distracted...say, falling off a cliff), Passive Perception is the absolute worst-case level of awareness for a given PC. The DM should constantly be applying passive scores to the environment.
Even in the stress of combat, participants are considered aware enough to bring their passive scores to bear against hidden enemies. Walking into a potential ambush situation (say, there's a dead horse and a suspicious leather purse on the road) is cake by comparison.
Having a low active roll supercede a higher passive score at best requires narrative contortions to explain away, and at worst creates disgruntled players who will struggle to find consistency in the rulings.
Passive Perception can be hard on the DM. It can wreck carefully planned encounters, and it makes ambushes very hard to pull off, especially in the era of bounded accuracy. It is, however, there for a good reason.
Rolling lower than your passive score would indeed be a conceptual problem, doing worse than what your minimum should be, if you were ever in a situation where you could use both kinds of check. But, by design, the two kinds of checks are used at different times, in different situations, so there is not a conflict. When one kind of check is being used, the other should not be.
In the case that Passive checks are used, they are for two completely different reasons, as explained in the PHB (emphases mine):
A passive check is a special kind of ability check that doesn't involve any die rolls. Such a check can represent the average result for a task done repeatedly, such as searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster...The rules on hiding in the “Dexterity” section below rely on passive checks, as do the exploration rules.
Taking the second use case first, since it is the one presented by the OP, Passive checks are used to contest Stealth specifically when the PC's are looking for hidden monsters. This is the general case when the DM does not want the players to know the results of rolls, often because the characters would not know the results of the attempt.
This is in contrast to a situation in which the characters will immediately know whether their attempt succeeded or failed. If I make an Athletics check to "jump an unusually long distance", there is no meta-information in the roll, because my character already knows whether they succeeded or failed. If I am looking for Hidden foes, however, and do not find them, I should not know whether I looked poorly and failed, or looked well but no foes were there.
Consider the following scenario - the party scout checks a colonnaded hall, where opportunities for Hidden foes abound. If the DM were to allow a Perception roll, the player would know what their character got, and metagaming could ensue. 'I rolled a 19, so I'm sure there's nothing here, let's move on.' vs. 'I rolled a ten - let's proceed cautiously, since there could be Hidden foes here.' Or, as they say in 3.5e, 'I think I just failed a Spot check.'
The point is that the player should not know 'how well they perceived' if they are then going to act on that meta-information. It is assumed that their character is always looking to the best of their ability, but doesn't know whether they failed or by how much they succeeded. Rather, they know they are a 'good scout' (based on their Passive score), and that they will see anything obvious or typically Hidden - but they have to assume that a very Stealthy foe will escape their notice. So when the DM says 'the hall appears empty', the player does not know whether that means there is actually nothing there, or that the things that are there are just very good at Hiding - which is precisely the information their character has.
In this case, it is not possible to roll 'under the floor' of the passive Perception, since if the DM is calling for passive Perception it is because they specifically do not want rolls to be made.
The other use case for passive Perception is for the average of 'a task done repeatedly'. Here, the DM would determine what 'repeatedly' means, and use a passive score in some cases, or call for a roll in others, but not both in the same situation.
Suppose the characters come upon a closed door. At this point they are being cautious in their explorations and the scout declares that they are going to listen at the door for several minutes. The DM decides that this is a task done repeatedly, and uses the scout's passive Perception to tell them what they hear - the muted conversation of the monsters within. There is no chance of 'rolling under the floor', because as soon as the DM determines that a passive score will be used, no roll is going to be made.
Now take the same characters, the same door, and the same monsters within. This time, however, the characters are being pursued and are just a few rounds ahead of their pursuers. Now the scout says 'I listen at the door, but if I don't immediately hear something, I open it and continue moving'. In this case the DM calls for a roll - the scout is spending their combat-round action on a Perception check. They might roll high and hear the monsters, or they might roll low and not. It would be unlucky for them to be listening during a six-second lull in the monster's conversation, but it could happen. If it did, they would not be rolling under their floor, because their floor presumes repeated attempts that average over time. In this case, they just get one shot, and sometimes that means they underperform compared to their typical ability.
Some characters "have refined [their] chosen skills until they approach perfection." For them, they are so reliably good, it is simply impossible for them to be very unlucky, even at a one-shot chance of something. In this case, their passive score is equivalent to the floor to their roll, but it is not the ceiling, because the DM has called for a roll, and there is a fair chance they will roll higher than the average. As Groody points out in his answer, this is the case for Rogues with Perception as their Reliable Talent. As the exception that proves the rule, assigning this class feature to this skill is valuable only because other characters can roll under what would be their passive 'floor' (were Passive scores allowed) in the same situation.
There is no conflict when a low Perception roll is under the passive Perception, because rolled and passive Perception should never occur in the same circumstances.
No, passive doesn't supersede active perception. They work mostly in parallel to each other.
What happens in passive perception is the object or event that is going to roll if they pass your perception and is actively hiding from you. The burden of rolling is on the object or event not on your PC. But when you start actively searching, the burden of rolling is on you and your PC.
However, you are correct in saying that the PC should have intuitively detected something for having a high perception. This now falls on the DM. Rolling a low roll doesn't automatically mean you see nothing, that's impossible in real life (unless you are blind/deaf). You sure see or hear something, but not explicitly the thing you are looking for. It may be a clue or a minor thing that should herald the discovery of the thing you want to detect. At this rate it's no longer a perception check but a Wisdom check, basically the DM should determine if your instincts would tell you "Hey! I think something is wrong!". This usually means a second die roll though some DMs like to determine it by looking at the PC's Wisdom score.
In your situation it can go like this: The scout rolls low so he doesn't see the hidden animals. But he did see that some of the foliage seemed disturbed, or there is a suspicious absence of sounds around him or even tracks. He has a high Wisdom score and proficiency in Perception so he was able to determine that a certain area seem to be a good place to hide... and ambush people passing by.
So basically you failed your active perception check for detecting the monsters but succeeded in your passive perception check in detecting clues that there are monsters around.
